Large off-highway vehicles (“OHVs”), such as mining vehicles used to haul heavy payloads excavated from open pit mines, may employ motorized wheels for propelling or retarding the vehicle in an energy efficient manner. In some such vehicles, this efficiency is obtained by employing a large-horsepower diesel engine in conjunction with an alternator and an electric drive system, which may include a main traction inverter and a pair of wheel drive assemblies housed within the rear tires of the vehicle. A drive shaft of the diesel engine is mechanically coupled to the alternator, for driving the alternator to generate electricity. The electricity generated by the alternator is routed to the main traction inverter, which supplies electrical power having a controlled voltage and frequency to electric drive motors of the two wheel drive assemblies. Each wheel drive assembly houses a planetary gear transmission that converts the rotation of the associated drive motor energy into a high-torque, low-speed rotational energy output which is supplied to the rear wheels.
Braking of these large OHVs is typically accomplished using a “blended” brake system, that is, a combination of the electric drive system and friction brakes associated with the front and rear wheels. In particular, the electric drive system may be utilized not only to propel the vehicle, but to apply retarding tractive effort to the rear wheels to effect braking of the vehicle, as desired. In addition, or alternatively, the front and rear friction brakes may be applied in certain situations to bring the vehicle to a stop or to maintain the position of the vehicle when stopped. As will be readily appreciated, depending on the specific circumstance or application, the electric drive system, the front friction brakes, and the rear friction brakes, or a combination of one or more of these braking elements, may be utilized for vehicle stopping and holding.
Operating loads in an OHV may exceed one hundred tons, while the gross weight of the vehicle and load may be several hundred tons. Operating these vehicles on grade and in wet conditions, therefore, can present challenges. In addition, operating such heavy vehicles in challenging conditions necessitates that the braking systems on board the vehicle operate efficiently and reliably to safely control vehicle speed and stopping, for example, to reduce or mitigate sliding and spinning conditions.